<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }
        
        .big {
            width: 500px;
            height: 500px;
            background-color: red;
            padding-left: 10px solied #000;
        }
        
        .small {
            width: 100px;
            height: 100px;
            background-color: blue;
            border: 10px solid chartreuse;
        }
        
        .box {
            width: 200px;
            height: 200px;
            background-color: chocolate;
            border: 5px solid #000;
        }
        /* option + sheft+ 下箭头 复制 */
        
        .top {
            width: 100px;
            height: 100px;
            background-color: blueviolet;
        }
        
        .bottom {
            width: 100px;
            height: 100px;
            background-color: red;
        }
        
        .father {
            width: 200px;
            height: 200px;
            background-color: saddlebrown;
            overflow:auto; 
        }
        
        .son {
            width: 50px;
            height: 50px;
            margin-top: 20px;
            background-color: sandybrown;
        }
    </style>
</head>

<body>
    <!-- <div class="big">
        <div class="small"></div>
    </div> -->
    <!-- <div class="top"></div>
   

    <div class="bottom"></div> -->

    <div class="father">
        <div class="son"></div>
    </div>
</body>

</html>